1. Field of the Invention
The present invention relates generally to amplifier gain profile control and calibration.
2. Background Art
Radio Frequency (RF) amplifiers, including broadband RF amplifiers, are typically designed to have flat gain, noise figure (NF), and linearity over their operating frequency range, as much as practically possible.
However, in many applications (e.g., cable television (CATV)), the input signal may not have equal power and density across the entire operating frequency range. As a result, when the input signal is amplified by a flat gain amplifier, weaker power components of the resulting amplified signal will have poorer signal-to-noise ratio (SNR) and signal-to-distortion ratio (SDR) than prior to amplification. Further, this degradation in SNR and SDR will continue in subsequent signal processing stages of the overall system.
There is a need therefore to amplify the input signal such that the resulting amplified signal has substantially uniform SNR and SDR across the entire operating frequency range. Further, since the input signal may vary over time, there is a need to adaptively shape the gain profile of the amplifier according to the input signal. At the same time, for best amplification performance, there is a need to accurately set and control the gain profile of an amplifier and to minimize gain profile variations due to temperature and/or process variations, for example.
Conventional solutions use multiple amplifiers with different gain profiles and switch from one amplifier to another according to the input signal to achieve the desired amplification. Clearly, however, these solutions are expensive and need to be designed with a priori knowledge or estimate of the input signal. Further, these solutions cannot guarantee the gain profile accuracy required by some applications or compensate for gain profile variations.